Urea Concentration Identification Device for Urea Solution

ABSTRACT

A urea concentration identification device comprising a concentration identification sensor unit ( 2 ) and a support unit ( 4 ) attached at the bottom end thereof with this sensor unit and provided at the top end thereof with a mounting unit ( 4   a ) to a urea solution tank opening. The concentration identification sensor unit ( 2 ) has an indirectly-heated concentration detector and liquid temperature detector provided with metal fins ( 21   c ),( 22   c ), respectively, for heat-exchanging with urea solution. The concentration identification sensor unit ( 2 ) is provided with a cover member ( 2   d ) that forms an opposite-ends-opened urea solution induction passage so as to surround the metal fins ( 21   c ),( 22   c ), and an enclosure ( 2   e ) that forms communication holes ( 26 ),( 27 ) in the top and bottom end plate thereof ( 2   e   1 ),( 2   e   2 ). A single-pulse voltage is applied to the heating element of the indirectly-heated concentration detector to heat it, and a urea concentration is identified at an identification operation unit based on an output from a concentration detection circuit including the temperature sensing element of the indirectly-heated concentration detector and the liquid temperature detector.

TECHNICAL FIELD

The present invention relates to a device for identifying a urea concentration in urea solution which is to be sprayed to exhaust purification catalyst so as to decompose nitrogen oxides (NOx) in a system to purify exhaust discharged from an internal-combustion engine of an automobile, etc.

BACKGROUND ART

In an internal-combustion engine of an automobile, fossil fuel such as gasoline or gas oil is burnt. Exhaust that is generated along with the combustion includes, together with water and carbon dioxide, environmental pollutants such as unburned carbon monoxide (CO) and carbon hydride (HC), sulfur oxides (Sox), and nitrogen oxides (NOx). Recently, especially for environmental protection and to prevent living environment from being polluted, there are suggested various countermeasures to purify exhaust from an automobile.

As one countermeasure, there is known the use of an exhaust purification catalyst device. According to this device, three way catalyst for exhaust purification is arranged on the way of an exhaust system, where CO, HC, NOx and the like are decomposed by oxidation-reduction to be rendered harmless. In order to continuously keep decomposing NOx in the catalyst device, urea aqueous solution is sprayed to the catalyst from the upstream side of the catalyst device of the exhaust system. The urea aqueous solution has to have its concentration set to be in a specific urea concentration range so as to enhance the effect of decomposing NOx, and particularly a urea concentration of 32.5% is considered to be most desirable.

Urea solution, which is stored in a urea solution tank carried on an automobile, may have its concentration changed as time goes by, and furthermore, there may be raised unevenness in concentration distribution locally in the tank. Urea solution, which is to be supplied to a spray nozzle from the tank through a supply-pipe by means of a pump, is generally taken out from an outlet port located near the bottom of the tank. Thus, urea solution around the area has to be of a desired urea concentration so as to enhance the efficiency of the catalyst device.

On the other hand, conventionally, a urea concentration in urea solution is not directly measured. Furthermore, in an exhaust system, there is employed a method of arranging NOx sensors at the upstream side as well as at the downstream side of a catalyst device, and judging whether or not decomposition of NOx is suitably carried out based on the difference of NOx concentrations detected by these sensors. However, this method is employed to measure the effect of actual reduction of NOx, and cannot identify a urea concentration not only before spraying urea solution but also from the very beginning of spraying urea solution. Moreover, NOx sensors used in this method are not sufficient in sensitivity for realizing spraying urea solution of a desired concentration.

In Patent Document 1, there is disclosed a fluid identification method of making a heating element generate heat by applying current thereto, heating a temperature sensing element using thus generated heat, exerting a thermal influence on heat transfer from the heating element to the temperature sensing element by means of fluid to be identified, and determining the kind of the fluid to be identified based on an electric output corresponding to an electric resistance of the temperature sensing element, in which method current is applied to the heating element periodically.

However, since current is applied to the heating element periodically (with multiple pulses), this fluid identification method is required to take considerable time for identification, which makes it difficult to identify the fluid instantly. Furthermore, under this method, even if fluid identification can be carried out using a representative value for materials whose properties are significantly different from each other such as water, air, oil, it is difficult to identify a urea concentration correctly and promptly by applying this method to the above-described urea concentration identification for urea solution.

Moreover, in order to improve the reliability of an exhaust purification processing system, it is desired that concentration identification for urea solution be carried out frequently and appropriate processing be performed. Accordingly, it may be necessary to carry out concentration identification for urea solution while an automobile is moving. Under this condition, identification precision is generally lowered as compared with that in the case under static condition. It is important to suppress the lowering of precision as much as possible to make it possible to correctly carry out concentration identification.

Patent Document 1: JP(A)-11-153561 (especially paragraphs [0042] to [0049])

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome the above-mentioned drawbacks by providing an identification device for urea solution which can identify a urea concentration in urea solution correctly as well as promptly.

Furthermore, the present invention has another object to provide an identification device for urea solution which can carry out concentration identification even under shaking condition.

According to the present invention, there is provided a urea concentration identification device for identifying a urea concentration in urea solution stored in a tank, comprising a concentration identification sensor unit; and a support unit having one end to which the concentration identification sensor unit is attached and the other end provided with a mounting unit to be attached to an opening of the tank,

wherein the concentration identification sensor unit includes an indirectly-heated concentration detector having a heating element and a temperature sensing element, and a liquid temperature detector for measuring the temperature of urea solution; the indirectly-heated concentration detector has a heat transfer member for concentration detector for exchanging heat with the urea solution; the liquid temperature detector has a heat transfer member for liquid temperature detector for exchanging heat with the urea solution; and a cover member is attached to the concentration identification sensor unit so as to surround the heat transfer member for concentration detector and the heat transfer member for liquid temperature detector to form a urea solution induction passage with its both ends opened, the urea solution induction passage extending in the longitudinal direction of the support unit, which is directed from one end to the other end thereof,

wherein the concentration identification sensor unit is provided with an enclosure which three-dimensionally encloses the periphery of the urea solution induction passage without covering both the ends of the urea solution induction passage; the enclosure is provided with a first communication hole and a second communication hole formed on one end plate and the other end plate thereof separated in the longitudinal direction, respectively; the first and second communication hole are located away from the extension of the urea solution induction passage so as to allow the urea solution to pass therethrough; and the second communication hole is so provided as to be separated away from a line which passes through the first communication hole and extends in the longitudinal direction, and

wherein a single-pulse voltage is applied to the heating element of the indirectly-heated concentration detector to make the heating element generate heat, and an identification operation unit identifies the urea concentration based on an output of a concentration detection circuit including the temperature sensing element of the indirectly-heated concentration detector and the liquid temperature detector.

According to an aspect of the present invention, the one end plate and the other end plate of the enclosure are separated away from both ends of the urea solution induction passage by 3 mm or more. According to an aspect of the present invention, the first communication hole and the second communication hole have their longer diameters set to be 10 mm or lower. According to an aspect of the present invention, the enclosure is in the form of a cylinder with the one end plate and the other end plate correspond to both end surfaces.

According to an aspect of the present invention, the identification operation unit identifies the urea concentration using a concentration correspondence voltage value corresponding to the difference between the initial temperature and the peak temperature of the temperature sensing element when the heating element generates heat. According to an aspect of the present invention, as a voltage value corresponding to the initial temperature of the temperature sensing element, an average initial voltage value which is obtained by sampling the initial voltage before starting the application of the single-pulse voltage to the heating element by a predetermined number of times and calculating the average thereof is used, and as a voltage value corresponding to the peak temperature of the temperature sensing element, an average peak voltage value which is obtained by sampling the peak voltage before ending the application of the single-pulse voltage to the heating element by a predetermined number of times and calculating the average thereof is used, and as the concentration correspondence voltage value, the difference between the average peak voltage value and the average initial voltage value is used.

According to an aspect of the present invention, a liquid temperature correspondence output value corresponding to the liquid temperature of the urea solution is input from the liquid temperature detector to the identification operation unit, and the identification operation unit identifies the urea concentration, using calibration curves indicative of the relation between the liquid temperature and the concentration correspondence voltage value prepared for a plurality of reference urea solutions whose urea concentrations are different from each other and given in advance, based on the liquid temperature correspondence output value and the concentration correspondence voltage value obtained for urea solution to be identified.

According to an aspect of the present invention, the identification operation unit has a microcomputer. According to an aspect of the present invention, a circuit board constituting the concentration detection circuit is arranged on the other end of the support unit, and a wire runs inside the support unit to electrically connect the concentration identification sensor unit to the circuit board. According to an aspect of the present invention, the microcomputer is arranged on a circuit board.

According to the present invention, since a urea concentration is identified for urea solution stored in a tank, a concentration identification sensor unit is arranged inside the tank, and urea concentration identification with desirable precision can be stably performed without being affected by external environmental conditions.

Furthermore, according to the present invention, since a urea concentration is identified at an identification operation unit based on an output of a concentration detection circuit by applying a single-pulse voltage to a heating element of an indirectly-heated concentration detector to make the heating element generate heat, a urea concentration in urea solution can be identified correctly as well as promptly. Especially, if a urea concentration is identified using a concentration correspondence voltage value corresponding to the difference between the initial temperature and the peak temperature of a temperature sensing element when the heating element generates heat, and the difference between an average peak voltage value and an average initial voltage value is used as the concentration correspondence voltage value, correct as well as prompt identification can be performed stably.

Furthermore, according to the present invention, since a cover member surrounds a heat transfer member for concentration detector and a heat transfer member for liquid temperature detector to from a urea solution induction passage with its both ends opened, urea-solution around the heat transfer members has difficulty in raising a forced flow based on a foreign factor, which can improve the precision of the above-described concentration identification.

Especially, according to the present invention, since an enclosure is arranged at a concentration identification sensor unit, and a first communication hole and a second communication hole are formed at specific positions on specific plates of the enclosure, lowering of the precision of identification can be reduced even if the tank is under shaking condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of one embodiment of the urea concentration identification device according to the present invention;

FIG. 2 shows a sectional view of the urea concentration identification device part of which is omitted;

FIG. 3 shows a view indicative of the state of mounting the urea concentration identification device to a tank;

FIG. 4 shows an enlarged view of an indirectly-heated concentration detector and a liquid temperature detector;

FIG. 5 shows a sectional view of the indirectly-heated concentration detector of FIG. 4;

FIG. 6 shows an exploded perspective view of a thin film chip of the indirectly-heated concentration detector;

FIG. 7 shows a block diagram of a circuit for identifying a concentration;

FIG. 8 shows a view indicative of the relation between a single-pulse voltage P applied to a heating element and a sensor output Q,

FIG. 9 shows an example of calibration curves;

FIG. 10 shows an example of a liquid temperature correspondence output value T;

FIG. 11 shows an example of the relation between a concentration correspondence voltage value V0 and an actual concentration;

FIG. 12 shows an example of the relation between a concentration correspondence analog output voltage value V0′ and an actual concentration;

FIG. 13 shows an example of the relation between a liquid temperature correspondence analog output voltage value T′ and an actual temperature;

FIG. 14 shows a result of an experiment carrying out concentration identification;

FIG. 15 shows a result of an experiment carrying out concentration identification;

FIG. 16 shows a result of an experiment carrying out concentration identification;

FIG. 17 shows a result of an experiment carrying out concentration identification;

FIG. 18 shows a result of an experiment carrying out concentration identification;

FIG. 19 shows a result of an experiment carrying out concentration identification; and

FIG. 20 shows a result of an experiment carrying out concentration identification;

wherein reference numeral 2 denotes a concentration identification sensor unit, 2 a basal body, 2 b,2 c O-ring, 2 d cover member, 2 e enclosure, 2 e 1 upper plate, 2 e 2 lower plate, 2 e 3 side plate, 21 indirectly-heated concentration detector, 22 liquid temperature detector, 23 mold resin, 24 urea solution induction passage, 26,27 communication hole, 21 a thin film chip, 21 b jointing material, 21 c,22 c metal fin, 21 d bonding wire, 21 e, 22 e external electrode terminal, 21 a 1 basal plate, 21 a 2,22 a 2 temperature sensing element, 21 a 3 inter-layer insulating film, 21 a 4 heating element, 21 a 5 heating element electrode, 21 a 6 protective film 21 a 7 electrode pad, 4 support unit, 6 circuit board, 8 cover member, 10,14 wire, 12 connector, 64, 66 resistor, 68 bridge circuit, 70 differential amplifier, 71 liquid temperature detection amplifier, 72 microcomputer, 74 switch, 76 output buffer circuit, 100 urea solution tank, 102 opening, 104 urea concentration identification device, 106 inlet pipe, 108 outlet pipe, 110 urea solution supply pump, and US denotes a urea solution.

BEST FOR CARRYING OUT THE INVENTION

The present invention will further be described below concerning the best modes with reference to the accompanying drawings.

FIG. 1 shows an exploded perspective view of one embodiment of the urea concentration identification device according to the present invention, FIG. 2 shows a sectional view of the same, part of which is omitted, and FIG. 3 shows a view indicative of the state of mounting the same to a tank.

As shown in FIG. 3, a urea solution tank 100 for decomposing NOx, which constitutes an exhaust purification system carried on an automobile, etc., is provided with an opening 102 on the top thereof, and a urea concentration identification device 104 according to the present invention is mounted to the opening 102. To the tank 100, an inlet pipe 106 from which urea solution is let in and an outlet pipe 108 from which urea solution is taken out are fixed. The outlet pipe 108 is coupled to the tank 100 at a height located near the bottom thereof, and is coupled to a urea solution spray unit, not shown, through a urea solution supply pump 110. In an exhaust system, the urea solution spray unit arranged right before an exhaust purification catalyst device sprays urea solution to the catalyst device.

The urea concentration identification device 104 includes a concentration identification sensor unit 2 and a support unit 4. The concentration identification sensor unit 2 is attached to one end (bottom portion) of the support unit 4, and the other end (top portion) of the support unit 4 is provided with a mounting unit 4 a to be attached to the opening 102 of the tank 100.

The concentration identification sensor unit 2 includes an indirectly-heated concentration detector 21 that has a heating element and a temperature sensing element, and a liquid temperature detector 22 that measures the temperature of urea solution. The indirectly heated concentration detector 21 and the liquid temperature detector 22 are arranged in the up and down direction with a predetermined distance situated therebetween. FIG. 4 shows an enlarged view of the indirectly-heated concentration detector 21 and the liquid temperature detector 22, and FIG. 5 shows a sectional view of the same.

As shown in those figures, the indirectly-heated concentration detector 21 and the liquid temperature detector 22 are united by a mold resin 23. As shown in FIG. 5, the indirectly-heated concentration detector 21 includes a thin film chip 21 a having a heating element and a temperature sensing element, a metal fin 21 c working as a heat transfer member for concentration detector which is coupled to the thin film chip 21 a through a jointing material 21 b, and external electrode terminals 21 e which are electrically connected to an electrode of the heating element and an electrode of the temperature sensing element of the thin film chip 21 a through a bonding wire 21 d. The liquid temperature detector 22 has similar structure, and includes a metal fin 22 c working as a heat transfer member for liquid temperature detector and external electrode terminals 22 e.

FIG. 6 shows an exploded perspective view of the thin film chip 21 a of the indirectly-heated concentration detector 21. For example, the thin film chip 21 a has a basal plate 21 a 1 made of Al₂O₃, a temperature sensing element 21 a 2 made of Pt, an inter-layer insulating film 21 a 3 made of SiO₂, a heating element 21 a 4 made of TaSiO₂ and a heating element electrode 21 a 5 made of Ni, a protective film 21 a 6 made of SiO₂, and electrode pads 21 a 7 made of Ti/Au, which are layered in this order. The temperature sensing element 21 a 2 is formed into a meandering pattern, which is not shown. The liquid temperature detector 22 has a thin film chip 22 a of similar structure, and does not make a heating element work but makes only a temperature sensing element 22 a 2 work.

As shown in FIG. 1 and FIG. 2, the concentration identification sensor unit 2 has a basal body 2 a mounted to the bottom end portion of the support unit 4, and O-rings 2 b are used when mounting the basal body 2 a. To the side of the basal body 2 a, the mold resin 23 uniting the indirectly-heated concentration detector 21 and the liquid temperature detector 22 is attached through an O-ring 2 c. To the basal body 2 a, a cover member 2 d is so attached as to surround the fin 21 c for concentration detector and the fin 22 c for liquid temperature detector. The cover member 2 d forms a urea solution induction passage 24 that extends in the up and down direction, passing through the fin 21 c for concentration detector and the fin 22 c for liquid temperature detector sequentially, with its both upper and lower ends opened. Since the cover member 2 d is attached to the basal body 2 a, a flange portion of the mold resin 23 is pressed toward the basal body 2 a, which fixes the mold resin 23 to the basal body 2 a.

On the top portion of the support unit 4, a circuit board 6 constituting a concentration detection circuit to be described later is arranged, and a cover member 8 is so mounted as to cover the circuit board 6. As shown in FIG. 2, inside the support unit 4, a wire 10 runs to electrically connect the indirectly-heated concentration detector 21 and liquid temperature detector 22 of the concentration identification sensor unit 2 to the circuit board 6. The circuit board 6 has a microcomputer arranged thereon that works as an identification operation unit to be described later. Through a connector 12 attached to the cover member B, a wire 14 is provided for carrying out communication between the circuit board 6 and the outside. The identification operation unit may be arranged not on the circuit board 6 but outside the cover member 8, in which case the circuit board 6 and the identification operation unit are connected through the wire 14.

As shown in FIG. 1 and FIG. 2, the concentration identification sensor unit 2 has an enclosure 2 e that three-dimensionally encloses the periphery of the urea solution induction passage 24, desirably with a predetermined distance of 3 mm or more situated therebetween, without covering both the upper and lower ends of the urea solution induction passage 24. The enclosure 2 e is in the form of a cylinder and has a planar upper plate 2 e 1, a planar lower plate 2 e 2, and a cylindrical side plate 2 e 3. The center portion of the upper plate 2 e 1 is coupled to the basal body 2 a by welding, etc. The upper plate 2 e 1 is provided with a first communication hole 26 through which urea solution can pass, while the lower plate 2 e 2 is provided with a second communication hole 27 through which urea solution can pass. These communication holes 26, 27 are located away from the extension of the urea solution induction passage 24, and the second communication hole 27 is so provided as to be separated away from a line which passes through the first communication hole 26 and extends in the longitudinal direction (up and down direction) of the support unit 4. For example, the communication holes, 26, 27 are circular openings whose diameters are 10 mm or lower, and in case the holes are openings other than circular openings, longer diameters are 10 mm or lower.

For example, the enclosure 2 e has its horizontal (X direction and Y direction) dimension (diameter) set to be 50 to 100 cm, and has its up and down dimension (height) set to be 80 to 150 cm. On the other hand, the urea solution induction passage 24 has its up and down dimension set to be 1 to 4 cm.

The enclosure 2 e prevents the inside of the urea solution induction passage 24 from being affected even if a flux is raised in urea solution in the tank 100 when the tank 100 is shaken, so that precision of concentration identification is not significantly lowered, which processing will be described later. In case the dimension of the enclosure 2 e is too large, a flux is easily raised in urea solution inside the enclosure 2 e undesirably. On the other hand, in case longer diameters of the communication holes 26, 27 are too large, a flux raised in urea solution is prone to affect the inside of the urea solution induction passage 24. Furthermore, in case the distance between both the upper and lower-ends of the urea solution induction passage 24 and the enclosure 2 e is too short, specifically less than 3 mm, identification precision is prone to be lowered.

The basal body 2 a, cover member 2 d, and enclosure 2 e of the concentration identification sensor unit 2, support unit 4, and cover member 8 are made of corrosion-proof material such as stainless steel.

FIG. 7 shows a block diagram for identifying a concentration in the present embodiment. The temperature sensing element 21 a 2 of the indirectly-heated concentration detector 21, the temperature sensing element 22 a 2 of the liquid temperature detector 22, and two resistors 64, 66 form a bridge circuit 68. An output of the bridge circuit 68 is input to a differential amplifier 70, and an output of the differential amplifier (also referred to as concentration detection circuit output or sensor output) is input to a microcomputer 72 that works as an identification operation unit through an A/D converter, not shown. Also, the microcomputer 72 receives a liquid temperature correspondence output value corresponding to the liquid temperature of urea solution from the temperature sensing element 22 a 2 of the liquid temperature detector 22 through a liquid temperature detection amplifier 71. On the other hand, the microcomputer 72 outputs a heater control signal to a switch 74 located on an electric pathway to the heating element 21 a 4 of the indirectly-heated concentration detector 21 to control the opening and closing of the switch.

Next, the performance of concentration identification in the embodiment will be explained.

When urea solution US is stored in the tank 100, the enclosure 2 e of the concentration identification sensor unit 2 and the urea solution induction passage 24 formed by the cover member 2 d are filled with the urea solution US. When the tank 100 remains stationary, the urea solution US not only in the urea solution induction passage 24 but also in the entire tank 100 substantial y does not flow.

When the microcomputer 72 sends the heater control signal to the switch 74 to close the switch 74 for a predetermined period of time (for example, four seconds), a single-pulse voltage P of a predetermined height (for example, 10V) is applied to the heating element 21 a 4 to make the heating element generate heat. At this time, as shown in FIG. 8, an output voltage (sensor output) Q of the differential amplifier 70 gradually increases when the voltage P is being applied to the heating element 21 a 4, and gradually decreases after the application of the voltage P to the heating element 21 a 4 is ended.

As shown in FIG. 8, the microcomputer 72 samples the sensor output by a predetermined number of times (for example, 256 times) for a predetermined time period (for example, for one second) before starting the application of voltage P to the heating element 21 a 4, and obtains an average initial voltage value V1 by carrying out an operation to obtain the average value thereof. The average initial voltage value V1 corresponds to the initial temperature of the temperature sensing element 21 a 2. Furthermore, as shown in FIG. 8, the microcomputer 72 samples the sensor output by a predetermined number of times (for example, 256 times) for a predetermined time period (for example, for one second) before ending the application of voltage P to the heating element 21 a 4, and obtains an average peak voltage value V2 by carrying out an operation to obtain the average value thereof. The average peak voltage value V2 corresponds to the peak temperature of the temperature sensing element 21 a 2. Then, the difference between the average initial voltage value V1 and the average peak voltage value V2 (=V2−V1) is obtained as a concentration correspondence voltage-value V0.

On the other hand, in the above-described method, calibration curves indicative of the relation between the temperature and the concentration correspondence voltage value V0 are obtained in advance with respect to several urea aqueous solutions (reference urea solutions) whose urea concentrations are given in advance, and thus obtained calibration curves are stored in a storage means of the microcomputer 72. FIG. 9 shows an example of the calibration curves. In this example, calibration curves are prepared for reference urea solutions whose urea concentrations are 0%, 20%, and 40%.

As shown in FIG. 9, since the concentration correspondence voltage value V0 depends on the temperature, when measuring a concentration of urea solution to be measured using the calibration curves, a liquid temperature correspondence output value T that is input from the temperature sensing element 22 a 2 of the liquid temperature detector 22 through the liquid temperature detection amplifier 71 is also used. FIG. 10 shows an example of the liquid temperature correspondence output value T. Such a calibration curve is also stored in the storage means of the microcomputer 72. Furthermore, FIG. 11 shows an example of the relation between the concentration correspondence voltage value V0 and an actual concentration obtained from urea solutions whose temperatures and urea concentrations are different from each other.

From the liquid temperature correspondence output value T obtained for urea solution to be measured, a temperature value “t” is obtained using the calibration curve shown in FIG. 10. Then, concentration correspondence voltage values V0 (0%; t), V0 (20%; t), and V0 (40%; t) corresponding to the temperature value “t” are obtained on the respective calibration curves shown in FIG. 9. Then, it is determined how much percentage of urea concentration corresponds to the concentration correspondence voltage value V0 (X; t) obtained for urea solution to be measured, by carrying out proportion operation using at least two of the concentration correspondence voltage values V0 (0%; t), V0 (20%; t), and V0 (40%; t), for example, V0 (20%; t) and V0 (40%; t), on the respective calibration curves. As described above, identification of a urea concentration can be carried out correctly as well as promptly (instantly). On the other hand, as the calibration curves shown in FIG. 9, those using the liquid temperature correspondence output value T instead of the temperature can be employed, which can omit storing the calibration curve shown in FIG. 10.

Then, a signal indicative of thus obtained concentration value is output to an output buffer circuit 76 shown in FIG. 7 through a D/A converter, not shown, and is then output to a main computer (ECU), not shown, for carrying out combustion control for an engine of an automobile as an analog output. FIG. 12 shows an example of the relation between an analog output voltage value V0′ corresponding to a concentration and an actual concentration. The difference with respect to temperature in this relation is small, which enables practical use. Furthermore, FIG. 13 shows an example of the relation between an analog output voltage value T′ corresponding to a liquid temperature and an actual temperature. The liquid temperature correspondence analog output voltage value T′ is also output to the main computer (ECU) On the other hand, signals indicative of the concentration value and the liquid temperature value are taken out as digital outputs according to need, and are input to devices for displaying, alarming, and other performances.

The above-described urea concentration identification for urea solution is based on the principle that there is a correlation between a kinetic viscosity of urea solution under natural convection and a sensor output. In order to enhance the precision of concentration identification, it is desirable that urea solution around the fin 21 c for concentration detector and fin 22 c for liquid temperature detector has difficulty in raising a forced flow based on a foreign factor as much as possible. From such a viewpoint, it is desirable to use the cover member 2 d, especially one having urea solution induction passage 24 extending in the up and down direction. The cover member 2 d works also as a protection member that prevents a foreign matter from coming into contact therewith.

As described above, it is considered that the optimal concentration of urea solution to be used in an exhaust purification system is 32.5%. Accordingly, setting a range between 25% to 40% as an appropriate range, an alarm may be given in case an identification result deviating from the appropriate range is obtained. Furthermore, in case urea in the tank is reduced and the urea solution induction passage 24 comes to be unfilled with urea solution, a concentration correspondence voltage value of urea solution significantly deviating from the appropriate range is obtained in identifying a concentration, in which case a required alarm may also be given. Similarly, in case liquid (for example, salt solution, coolant water, etc.) whose correlation between a kinetic viscosity thereof and a sensor output is different from that of urea solution is poured into the tank by accident, a concentration correspondence voltage value different from that within the appropriate range which is obtained when using urea solution whose liquid temperature is equal to that of thus poured liquid is obtained in identifying a concentration, in which case a required alarm may also be given.

Furthermore, based on the liquid temperature correspondence output value T sent from the liquid temperature detector 22, in case it is detected that urea solution has its temperature reduced to a temperature around which urea solution is frozen (around −13° C.), an alarm may be given.

As in the above, the case in which the urea solution US in the tank 100 is not made to forcibly flow is explained. On the other hand, in case concentration identification is carried out when an automobile carrying the tank 100 is moving, there may be raised a flow in the urea solution due to the shaking of the tank 100. In this case, according to the device of the present invention, since the concentration identification sensor unit 2 has the enclosure 2 e, even if urea solution outside the enclosure is made to flow, an influence resulting from the flow is hardly exerted on the inside of the enclosure 2 e, especially on the inside of the urea solution induction passage 24.

Concerning the shaking of the tank 100, there is shaking in the up and down direction and shaking in the horizontal direction, and shaking which largely exerts an influence on the above-described concentration identification is shaking in the horizontal direction. This is because shaking in the horizontal direction largely contributes to liquid level fluctuation and urea solution flow resulting therefrom. The concentration identification sensor unit 2 is arranged near the bottom of the tank, at which height the flow of urea solution has little up and down direction components and dominating horizontal direction components. Accordingly, by forming a communication hole, which is not too large, on each of the upper plate 2 e 1 and the lower plate 2 e 2 of the enclosure 2 e to enable urea solution to pass therethrough between the outside of the enclosure and the inside of the enclosure, and forming no hole on the side plate 2 e 3, a flow in the horizontal direction of liquid inside the tank and outside the enclosure is prevented from exerting an influence on the inside of the enclosure.

Furthermore, at a position where the concentration identification sensor unit 2 is arranged, there exits a flow of urea solution in the up and down direction, which is not dominating. In this regard, by making positions of the communication holes 26, 27 different from each other in the horizontal plane (in the XY plane), urea solution is prevented from passing through the enclosure 2 e and flowing in the up and down direction. Moreover, by making positions of the communication holes 26, 27 different from that of the urea solution induction passage 24 in the horizontal plane (in the XY plane), a flow in the up and down direction is prevented from exerting an influence on the inside of the urea solution induction passage 24, FIG. 14 to FIG. 20 show results of experiments carrying out concentration identification using the concentration identification device according to the present invention or a device which are used for comparison. In these experiments, the enclosure is used or not used, and the number and arrangement of the communication holes formed at the enclosure are different, and the others in structure of the devices are made equal. Four liters of urea solution having urea concentration of 32.5% is used. Concentration values measured under various shaking speed conditions with amplitude of 40 mm in the X direction and Y direction are shown.

In an experiment shown in FIG. 14, as the communication holes 26, 27 formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm in diameter which are located at positions different from each other and also different from that of the urea solution induction passage 24 in the XY plane (horizontal plane) are formed, one for each plate respectively. Distances between the upper and lower end openings of the urea solution induction passage 24 and the upper and lower plates 2 e 1, 2 e 2 of the enclosure are set to be 5 mm, respectively. This experimental configuration is of the present invention.

In an experiment shown in FIG. 15, the enclosure is not used.

In an experiment shown in FIG. 16, as the communication holes 26, 27 formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm in diameter which are located at positions equal to that of the urea solution induction passage 24 in the XY plane (horizontal plane) are formed, one for each plate respectively. Distances between the upper and lower end openings of the urea solution induction passage 24 and the upper and lower plates 2 e 1, 2 e 2 of the enclosure are set to be 5 mm, respectively.

In an experiment shown in FIG. 17, as the communication holes 26, 27 formed at the upper plate 2 e 1 and lower plate 2 e 2, holes equal to those employed in the experiment shown in FIG. 14 are formed. On the other hand, distance between the lower end opening of the urea solution induction passage 24 and the lower plate 2 e 2 of the enclosure is set to be 5 nm, while distance between the upper end opening of the urea solution induction passage 24 and the upper plate 2 e 1 of the enclosure is set to be 0 mm (that is, the upper end of the urea solution induction passage is covered).

In an experiment shown in FIG. 18, as the communication holes 26, 27 formed at the upper plate 2 e 1 and lower plate 2 e 2, holes of 5 mm in diameter which are located at positions different from each other and also different from that of the urea solution induction passage 24 in the XY plane (horizontal plane) are formed, three for each plate respectively. Distances between the upper and lower end openings of the urea solution induction passage 24 and the upper and lower plates 2 e 1, 2 e 2 of the enclosure are set to be 5 mm, respectively.

In an experiment shown in FIG. 19, as the communication holes 26, 27 formed at the upper plate 2 e 1 and lower plate 2 e 2, holes equal to those employed in the experiment shown in FIG. 18 are formed. On the other hand, distance between the lower end opening of the urea solution induction passage 24 and the lower plate 2 e 2 of the enclosure is set to be 5 mm, while distance between the upper end opening of the urea solution induction passage 24 and the upper plate 2 e 1 of the enclosure is set to be 0 mm (that is, the upper end of the urea solution induction passage is covered).

In an experiment shown in FIG. 20, the experimental configuration is equal to that of the experiment shown in FIG. 19 except that there is formed no communication hole at the lower plate 2 e 2 and three communication holes 27′ are formed at the side plate 2 e 3.

As can be seen from the above-described results, in the experiments shown in FIG. 15 to FIG. 20, measurement values are widely distributed as compared with those in the experiment shown in FIG. 14 (measurement values 25% to 40%). Thus, it can be seen that the lowering of precision can be lessened according to the configuration of the present invention, even if the tank is shaken. 

1-10. (canceled)
 11. A urea concentration identification device for identifying a urea concentration in urea solution stored in a tank, comprising: a concentration identification sensor unit; and a support unit having one end to which the concentration identification sensor unit is attached and the other end provided with a mounting unit to be attached to an opening of the tank, wherein the concentration identification sensor unit includes an indirectly-heated concentration detector having a heating element and a temperature sensing element, and a liquid temperature detector for measuring the temperature of urea solution, the indirectly-heated concentration detector has a heat transfer member for concentration detector for exchanging heat with the urea solution, the liquid temperature detector has a heat transfer member for liquid temperature detector for exchanging heat with the urea solution, and a cover member is attached to the concentration identification sensor unit so as to surround the heat transfer member for concentration detector and the heat transfer member for liquid temperature detector to form a urea solution induction passage with its both ends opened, the urea solution induction passage extending in the longitudinal direction of the support unit, which is directed from one end to the other end thereof, wherein the concentration identification sensor unit is provided with an enclosure which three dimensionally encloses the periphery of the urea solution induction passage without covering both the ends of the urea solution induction passage, the enclosure is provided with a first communication hole and a second communication hole formed on one end plate and the other end plate thereof separated in the longitudinal direction, respectively, the first and second communication hole are located away from the extension of the urea solution induction passage so as to allow the urea solution to pass therethrough, and the second communication hole is so provided as to be separated away from a line which passes through the first communication hole and extends in the longitudinal direction, and wherein a single-pulse voltage is applied to the heating element of the indirectly-heated concentration detector to make the heating element generate heat, and an identification operation unit identifies the urea concentration based on an output of a concentration detection circuit including the temperature sensing element of the indirectly-heated concentration detector and the liquid temperature detector.
 12. The urea concentration identification device for the urea solution as claimed in claim 11, wherein the one end plate and the other end plate of the enclosure are separated away from both ends of the urea solution induction passage by 3 mm or more.
 13. The urea concentration identification device for the urea solution as claimed in claim 11, wherein the first communication hole and the second communication hole have their longer diameters set to be 10 mm or lower.
 14. The urea concentration identification device for the urea solution as claimed in claim 11, wherein the enclosure is in the form of a cylinder with the one end plate and the other end plate correspond to both end surfaces.
 15. The urea concentration identification device for the urea solution as claimed in claim 11, wherein the identification operation unit identifies the urea concentration using a concentration correspondence voltage value corresponding to the difference between the initial temperature and the peak temperature of the temperature sensing element when the heating element generates heat.
 16. The urea concentration identification device for the urea solution as claimed in claim 15, wherein as a voltage value corresponding to the initial temperature of the temperature sensing element, an average initial voltage value which is obtained by sampling the initial voltage before starting the application of the single-pulse voltage to the heating element by a predetermined number of times and calculating the average thereof is used, and as a voltage value corresponding to the peak temperature of the temperature sensing element, an average peak voltage value which is obtained by sampling the peak voltage before ending the application of the single-pulse voltage to the heating element by a predetermined number of times and calculating the average thereof is used, and as the concentration correspondence voltage value, the difference between the average peak voltage value and the average initial voltage value is used.
 17. The urea concentration identification device for the urea solution as claimed in claim 15, wherein a liquid temperature correspondence output value corresponding to the liquid temperature of the urea solution is input from the liquid temperature detector to the identification operation unit, and the identification operation unit identifies the urea concentration, using calibration curves indicative of the relation between the liquid temperature and the concentration correspondence voltage value prepared for a plurality of reference urea solutions whose urea concentrations are different from each other and given in advance, based on the liquid temperature correspondence output value and the concentration correspondence voltage value obtained for urea solution to be identified.
 18. The urea concentration identification device for the urea solution as claimed in claim 11, wherein the identification operation unit has a microcomputer.
 19. The urea concentration identification device for the urea solution as claimed in claim 11, wherein a circuit board constituting the concentration detection circuit is arranged on the other end of the support unit, and a wire runs inside the support unit to electrically connect the concentration identification sensor unit to the circuit board.
 20. The urea concentration identification device for the urea solution as claimed in claim 18, wherein the microcomputer is arranged on a circuit board.
 21. A urea concentration identification device for identifying a urea concentration in urea solution stored in a tank, comprising: a concentration identification sensor unit; a support unit having one end to which the concentration identification sensor unit is attached and the other end provided with a mounting unit to be attached to an opening of the tank; and a urea solution induction passage extending in the longitudinal direction of the support unit and having an opening on one side and an opening on the other side, wherein the concentration identification sensor unit is provided with an enclosure which three dimensionally encloses the periphery of the urea solution induction passage without covering both the ends of the urea solution induction passage.
 22. The urea concentration identification device for the urea solution as claimed in claim 21, wherein the enclosure is provided with a first communication hole and a second communication hole formed on one end plate and the other end plate thereof separated in the longitudinal direction of the support unit, respectively, the first and second communication hole are located away from the extension of the urea solution induction passage so as to allow the urea solution to pass therethrough, and the second communication hole is so provided as to be separated away from a line which passes through the first communication hole and extends in the longitudinal direction.
 23. The urea concentration identification device for the urea solution as claimed in claim 21, wherein the enclosure is free of side holes through which the sensor unit is visible from outside.
 24. The urea concentration identification device for the urea solution as claimed in claim 21, wherein the enclosure comprises an upper end plate, a side plate and a lower end plate, and the side plate has no hole.
 25. The urea concentration identification device for the urea solution as claimed in claim 22, wherein the enclosure is free of side holes through which the sensor unit is visible from outside.
 26. The urea concentration identification device for the urea solution as claimed in claim 22, wherein the enclosure comprises an upper end plate, a side plate and a lower end plate, and the side plate has no hole. 